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Estimation of mass transfer rate and primary drying times during freeze-drying of frozen maltodextrin solutions based on x-ray μ-computed tomography measurements of pore size distributions
- Foerst, Petra, Melo de Carvalho, Teresa, Lechner, Martin, Kovacevic, Tijana, Kim, Seongshik, Kirse, Christoph, Briesen, Heiko
- Journal of food engineering 2019 v.260 pp. 50-57
- annealing, cakes, cooling, diffusivity, freeze drying, freezing, geometry, maltodextrins, mass transfer, micro-computed tomography, porosity
- The study presents a method to estimate the mass transfer rate during primary drying based on μ-computed tomographic measurements of a freeze-dried cake. The study was carried out in a defined setup in a lyomicroscope and confined geometry in which freezing occurred under homogeneous nucleation, and drying under mass-transfer-limited conditions. Pore size distribution, effective diffusivity, and primary drying rates of maltodextrin solutions at different weight concentrations (5%, 10%, and 20% (w/w)) and different cooling rates were determined. Furthermore, the effect of annealing treatment on primary drying rate was studied. Two different annealing treatments were tested, one for 90 min at −10 °C and another for 180 min at −5 °C. It was shown that solid concentration and annealing above Tg’ have the strongest impact on pore size and, subsequently, on primary drying rate. Therefore annealing represents a powerful tool to accelerate primary drying which is the most time-consuming step during lyophilisation.